If he plays Zen appropriately, no problem.
On role queue beta, I would see many suspected Dps-main taking support and using Zen. The bad ones can be seen quickly by showing their DPS metalities and forgetting Zen’s role and weakness.
Things like pushing ahead of their tank line, wandering off on their own, exposing self to being dived on , solo Ulting to save own skin , things that elim-focued dps mains would do but not team-focused players familar with Zen play.
I feel disgust because it puts pressure on our other healer to pick up the slack and if they run flankers we lose.
TLDR “i hope he doesnt waste trans” 
Im dps main. i love zen and a skilled meta. better player wins. not slow drawn out moira fights.
just swap if u get hunted and again, make sure we get value out of trans
Since I’m mostly a Lucio-main, the 1st thing I think of is whether or not we (me and Zen) can sustain our team. I then think of which primary healer I should pick if healing isn’t enough.
In most of the cases, Moira ends up being the dominant healer role (for me), even though I feel like I do very well as healing with Lucio.
I have most of my hours played on Zen, but I’ve unabashedly fallen head over heals with Lucio’s playstyle.
So as a fellow (mostly secondary) support player, I’m not too miffed when I see someone pick Zen. I just think of how else I can help out the team composition.
“Time to damage-boost him like hell, because boy will we need that trans soon”.
Hey - that guy picked Zen.